(81c) Design of Biomass Pyrolyzer-Multiple Effect Distillation System Components for Laboratory Testing

Multiple effect distillation (MED) is among the most reliable thermal water desalination technologies. MED is driven by low pressure steam, as well as a small portion of electricity (pumps), which makes it attractive for replacing fossil fuel energy with a renewable energy source such as geothermal or biomass. Our overall project is the development of a pilot-scale biomass slow pyrolyzer-MED system in which the thermal and electrical energy needed to operate the MED unit comes from the biomass; the interface includes a burner to convert low-energy bio-oil and syngas into thermal energy, a boiler to produce superheated steam, and a steam turbine generator to produce electricity. The low-grade steam exiting the turbine generator is used as the primary steam for the first effect in the MED. In order to obtain data needed in the system model, we have constructed various lab-scale components to represent unit operations in the whole system.

The slow pyrolysis unit operation is represented with a batch, 10 L tube reactor designed to operate around at 400°C under a nitrogen environment and slow heating rates. We have used this reactor to produced biochar from locally-available, representative biomass feedstocks: pecan orchard prunings, pecan shells, cotton gin trash, tumbleweeds, and yard waste. We designed a burner to combust the pyrolysis exhaust gases for emissions control (and later heat generation), but due to current space limitations in the fume hood, we use an ice-bath condenser to collect the pyrolysis vapors. We have sourced a steam generator will replace the burner supplying heat for the MED unit. The MED lab-scale unit consists of three falling film evaporators in a forward feed arrangement with pre-heaters, able to produce approximately 20 kg/hr (20 L/hr) of distilled water.